Topic 15 - Transition Metals Flashcards
(36 cards)
What is a transition metal?
An element that forms one or more stable ions with incompletely filled d orbitals
What is a ligand?
A species that uses a lone pair of electrons to form a dative covalent bond with a metal ion
Why do transition metals have variable oxidation states?
Because they have a large number of unpaired electrons in their d orbitals allowing them to bond to many other molecules in different ways
Why do transition metals form coloured compounds?
Because the d orbitals occupy different energy levels, different transition metal species absorb different wavelengths of energy to excite electrons on lower energy levels to a higher one.
Why do some transition metals not form coloured compounds?
Because they have either no electrons in, or a full d sub shell, and therefore no room for electrons to be excited
What is a coordination number?
The coordination number is the number of dative bonds in a complex
What is a monodentate ligand?
A monodentate ligand forms only one dative bond to the central ion of a complex
Give an example of a square planar complex ion
Cisplatin Cl2Pt(NH3)2
Why is cis-platin used as a cancer treatment, but not trans-platin?
Because while cis-platin prevents the DNA in cancer cells from dividing, preventing mitosis, trans-platin has a different structure, and so is less effective and more toxic.
What is the colour of V5+ (VO2^+)?
Yellow
What is the colour of V4+ (VO^2+)?
Blue
What is the colour of V3+?
Green
What is the colour of V2+?
Purple
How can the dichromate ion be reduced to Cr2+?
In acidic conditions:
Cr2O7 2- +14H+ + 3Zn –> 2Cr3+ + 7H2O + 3Zn2+
2Cr3+ + Zn –> 2Cr2+ + Zn2+
How can the dichromate ion be converted into chromate ions?
Cr2O72−+ H2O ⇌ 2CrO42−+ 2H+
How can chromium(III) ions be oxidised to chromate ions?
2Cr(OH)3 + 3H2O2 +4OH- –> 2CrO4 2- + 8H2O
Describe the reactions that would occur when [Fe(H2O)6]2+ reacts with NaOH, and NaOH in excess
The initial reaction would, from the green solution, form a green precipitate of [Fe(H2O)4(OH)2], that would darken to brown on standing as it oxidises to [Fe(H2O)3(OH)3]. The excess would cause no further reaction.
Describe the reactions that would occur when [Fe(H2O)6]2+ reacts with NH3, and NH3 in excess
The initial reaction would form a green precipitate from the green solution of [Fe(H2O)4(OH)2] and ammonium ions. The precipitate would darken to brown as it oxidises to [Fe(H2O)3(OH)3]. The excess would cause no further reaction.
Describe the appearance of aqueous Fe3+ ions
[Fe(H2O)6]3+ appears pale violet in solution, but can appear orange due to hydrolysis to [Fe(H2O)5(OH)]2+
Describe the reactions that would occur when [Fe(H2O)6]3+ reacts with NaOH, and NaOH in excess
The initial reaction would, from the violet or orange solution, form a brown precipitate of [Fe(H2O)3(OH)3], The excess would cause no further reaction.
Describe the reactions that would occur when [Fe(H2O)6]3+ reacts with NH3, and NH3 in excess
The initial reaction would, from the violet or orange solution, form a brown precipitate of [Fe(H2O)3(OH)3] and ammonium ions, The excess would cause no further reaction.
Describe the reactions that would occur when [Cu(H2O)6]2+ reacts with NaOH, and NaOH in excess
The initial reaction would, from the blue solution, form a blue precipitate of [Cu(H2O)4(OH)2]. The excess would cause no further reaction.
Describe the reactions that would occur when [Cu(H2O)6]2+ reacts with NH3 and NH3 in excess
The initial reaction would, from the blue solution, form a blue precipitate of [Cu(H2O)4(OH)2]. The excess would cause a reaction producing a deep blue solution of [Cu(H2O)2(NH3)4]2+.
Define amphoteric behaviour
The ability of a species to react with both acids and bases
